It is highly desirable in knit fabrics to have the stitch loops as uniform as possible. Various changeable conditions affect the size and volume of the stitch loops being formed on a circular knitting machine. Examples of such changeable conditions include the tension in the yarn being fed to the needles, the stroke of the needles and the speed of rotation of the cylinder.
One way to control the tension in the yarn and thus the stitch volume is to adjust the yarn-feeding speed. One such known device is disclosed in JP-B-3-72738 (1991). While somewhat effective, this device is complicated, complex in that it embodies many components and costly to manufacture. Therefore, it has not been found to be a solution to the problem.
Another approach to controlling stitch size and volume is to adjust the size of the stitch loops by raising and lowering the stitch cam support to vary the stroke of the needles during stitch formation. Examples of such stitch loop adjusting mechanisms are disclosed in U.S. Pat. Nos. 5,174,133 and 5,511,392. In both of these prior mechanisms, feeding characteristics of the yarn or yarns, such as yarn tension or quantity of yarn fed, are measured and the stitch cam height adjusted responsive to the differential in that measurement and a pre-set value. While more effective than previous attempts, these mechanisms relied primarily upon only one or two of the variables on changeable conditions affecting stitch size or volume and were therefore limited in their responsiveness and in the improvements in fabric quality they could achieve.